Combustion engines such as gas turbine engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor.
A variety of combustor designs exist, with different designs being selected for suitability with a given engine and to achieve desired performance characteristics. One popular combustor design includes a centralized pilot burner (hereinafter referred to as a pilot burner or simply pilot) and several main fuel/air mixing apparatuses, generally referred to in the art as injector nozzles, arranged circumferentially around the pilot burner. With this design, a central pilot flame zone and a mixing region are formed. During operation, the pilot burner selectively produces a stable flame that is anchored in the pilot flame zone, while the fuel/air mixing apparatuses produce a mixed stream of fuel and air in the above-referenced mixing region. The stream of mixed fuel and air flows out of the mixing region, past the pilot flame zone, and into a main combustion zone of a combustion chamber, where additional combustion occurs. Energy released during combustion is captured by the downstream components to produce electricity or otherwise do work.
It is known that high frequency pressure oscillations may be generated from the coupling between heat release from the combustion process and the acoustics of the combustion chamber. If these pressure oscillations, which are sometimes referred to as combustion dynamics, or as high frequency dynamics, reach a certain amplitude they may cause nearby structures to vibrate and ultimately break. A particularly undesired situation is when a combustion-generated acoustic wave has a frequency at or near the natural frequency of a component of the gas turbine engine. Such adverse synchronicity may result in sympathetic vibration and ultimate breakage or other failure of such component.
Various resonator boxes for the combustion section of a gas turbine engine have been developed to damp such undesired acoustics and reduce the risk of the above-noted problems. For example, U.S. Pat. No. 6,837,051, issued Jan. 4, 2005 to Mandai et al., teaches a side wall defining a combustion volume, the side wall including a plurality of oscillation damping orifices downstream of the main nozzles and extending radially through the side wall, wherein acoustic liners of various configurations are attached to the side wall's outer surface over the location of the orifices, forming acoustic buffer chambers. Also, an arrangement of a more upstream disposed inner tube and a more downstream disposed combustor tail tube provides a film of air that is stated to reduce the fuel-air ratio adjacent the inner surface of the combustor tail tube and restrain combustion-driven oscillation.
U.S. Pat. No. 7,080,514, issued Jul. 25, 2006 to Robert Bland and William Ryan, teaches resonators for a gas turbine engine combustor that each comprise a scoop disposed above a respective resonator. The scoop is stated to capture passing fluid to substantially equalize pressure impinging a resonator plate of the resonator. This is stated to allow more design freedom by allowing for a greater pressure drop across the resonator.
U.S. Pat. No. 7,089,741, issued Aug. 15, 2006 to Ikeda et al., teaches forming a resonance space about a wall of a combustion liner that defines a combustion region. The resonance space connects to the combustion region by a plurality of through-holes. Additionally, cooling holes are provided along the sides of housings that help define the resonance space, stated as desirable along an upstream side and also shown along a downstream side. Purge holes also are provided along a more radially outwardly disposed surface.
While the above approaches may provide one or more favorable features, to address undesired combustion-generated acoustic waves there still remains in the art a need for a more effective and efficient resonator, and for a gas turbine engine comprising such resonator.